Looks like it follows Nationals standard circuit, should sound "normal". Would not recommend them for a BPA300 design cause they dont have any output resistors, no zobel network and no DC-circuit. They would most likely oscillate (spelling?), overheat and burn if paralleled.

Im working on a pair of boards, not finnished yet. Might order in a week or so.

coldfuzion76

14th March 2008 05:36 AM

yeah, i knew about the output resistors, was going to add them externally. I'm new to this stuff, though and didn't know about the other stuff. I actually originally started out just going to build a simple amp, but then I got this great deal on a dual center tapped 1000va transformer, and I got some killer older 12" Kenwoods to drive now. Figured I needed to ramp it up a bit.

Tripmaster

14th March 2008 03:06 PM

Gainclone PCBs

I am hoping some of you may be able to help. I am new to Gainclones and electronics.

Does any one know if I can buy the Chipamp.com or Audiosector.com PCBs in the UK? It would be easier to follow one of these kits.

I am really keen to make my own PCBs if someone has a simple yet reliable PCB design I could use.

I have purchased some copper boards and intend using the photo glossy paper method.

B&W DM601 S2
Crossover is at 4 kHz, efficiency is rated at 88dB/1W/1m, Impedance is said to be 8 Ohms nominal, 4.3 Ohms minimum
Response 70Hz-20kHz +/- 3dB on axis
Harmonic distortion below 1% 88-20.000 Hz at 90dB SPL at 1m.
Power handling is said to be 25-100W continuous of unclipped programme into 8 Ohms nominal

I really appreciate your help.

jackinnj

14th March 2008 03:12 PM

without a 100nF/3.3R zobel or 1uH/10R low pass filter that LM3875 amp, configured as it is on the PCB, will definitely oscillate.

coldfuzion76

15th March 2008 05:34 PM

Ok, so here's a question. I already have a couple of Peter Daniel's boards. If I got some more of those and used the Zobel option, and then added the output resistors externally, would that prevent the oscillation? I may not go for the full 300, I was thinking more of only using 4 chips per channel.

jackinnj

15th March 2008 06:06 PM

Quote:

Originally posted by coldfuzion76 Ok, so here's a question. I already have a couple of Peter Daniel's boards. If I got some more of those and used the Zobel option, and then added the output resistors externally, would that prevent the oscillation? I may not go for the full 300, I was thinking more of only using 4 chips per channel.

Yes, you can use the inductor externally -- it (or the Zobel) should be close to the LM3875 or LM3886.

Use a 1/2 dowel as a form to wind 10 turns of #18 magnet wire as the inductor -- you can even use RS PVC insulated wire -- slip a 10 ohm resistor through the coil -- this will lower the coil's "Q" dramatically

vectorplane

31st March 2008 07:23 AM

Quote:

Originally posted by CJ900RR ... dont have any output resistors, no zobel network and no DC-circuit. They would most likely oscillate... if paralleled.

\

What do you mean by "DC-circuit" ?

I'm reading the National literature, trying to understand this, but they don't mention any DC circuit.

CJ900RR

31st March 2008 09:09 AM

Quote:

Originally posted by vectorplane

What do you mean by "DC-circuit" ?

I'm reading the National literature, trying to understand this, but they don't mention any DC circuit.

Sorry, my bad. I should have written "servo circuit" witch is the correct name for it. Instead of using cap's to minimize DC-offset, you can use OP-amps to keep it low. Look at Nationals AN-1192 (http://www.national.com/an/AN/AN-1192.pdf) at page 13.